Sequence of Events
Shortly after takeoff, as the flight climbed through 3,100 feet, the No. 1 engine fire warning activated. About 20 seconds later, the captain, who was the pilot flying, moved the No. 1 throttle to idle and asked the first officer to declare an emergency with air traffic control. Approximately 47 seconds after the first officer identified the warning, the captain requested the engine fire emergency procedures checklist. The engine fire warning system deactivated about 88 seconds after activation due to fire damage to one of the fire loops. This occurred 2 seconds before the first officer moved the No. 1 fuel lever to the off position, shutting down the engine. The flight crew did not notice the warning that the No. 1 fire loop system was inoperative.
The engine fire warning system uses two loops. If one loop becomes inoperative because of fire damage, the warning deactivates and a fire loop warning is displayed. The crew must deactivate the faulty loop to regain the warning. The crew stopped the procedure after shutting down the No. 1 engine because the fire light went out, and therefore did not activate the No. 1 fire handle. Pressurized fuel continued to be supplied to the engine, feeding the fire.
The flight crew turned back to the departure airport. At 2,000 feet, about 3 minutes from landing, a flight attendant reported that a mechanic in the back had stated that the No. 1 engine was still smoking or on fire. The flight crew did not take any action and landed. About 1 minute after stopping, the captain ordered an emergency evacuation of the airplane, with instructions not to use the left overwing exits. About 1 minute 55 seconds after landing, the flight crew pulled the engine and auxiliary power unit fire handles and discharged the fire bottles into the No. 1 engine.
Procedural Context
In 1995, Airbus changed the engine fire procedure to allow discontinuing the fire procedure and keeping an engine running at idle after an engine fire warning once the warning has gone out and the throttle has been moved to idle. This change was made because of the high number of bleed air leak activated fire warnings.
Post-Incident Examination
Postincident examination of the No. 1 engine showed that all the accessory gearbox idler adapter attachment bolt inserts had backed out, allowing fuel lines to unseat and spray pressurized fuel onto hot engine parts and ignite. On September 26, 1995, the accessory gear box idler adapter had been reworked per General Electric Aircraft Engine Service Bulletin 72-743 during engine overhaul at a vendor's facility. Smaller-than-required adapter bolt inserts had been installed.